Composition and method for producing protective coatings



COMPOSITION AND METHOD FOR PRODUCING PROTECTIVE COATINGS Bertha S. Tuttle, Newton, Walter A. Vittands, Jamaica Plain, and Orren L. Walsh, Melrose, Mass., assignors, by mesne assignments, to Second Bank-State Street Trust Company, Boston, Mass., a corporation of Massachusetts No Drawing. Application August 19, 1954 Serial No. 451,053

19 Claims. (Cl. 148-614) In treating phosphate coated surfaces by the process disclosed in United States Patent 2,478,954, dated August 16, 1949, stannous salts are used, particularly the chloride. Due to the high acidity of commercially available stannous chloride, it is necessary partially to neutralize the treating solution and add stabilizers in order to achieve the desired results. The use of buffers, stabilizers and the like adjuvants is apt to introduce other difliculties such as excessive sludge formation, impairment of the efiicacy of the treatment, etc., and consequently the treating solution must be carefully prepared and periodically checked. Moreover, it is not feasible to supply the constituents of a treating solution to the user either separately or admixed, since there is no assurance that those charged with carrying out of the treating operation are sufficiently competent to prepare a satisfactory treating solution and maintain it in usable condition. Hence, trained personnel must be available to oversee the preparation and proper use of the treating solution.

The principal objects of the present invention are to overcome the aforementioned difliculties and to provide a stable composition containing the necessary ingredients which may be readily mixed with a prescribed amount of water to produce a stable treating solution having the correct pH, solids content etc., and which does not undergo deterioration or change after a reasonably long period of use, thereby to enable an unskilled operator to practice the above-identified process merely by observing temperature and time of treatment.

Further objects will be apparent from the consideration of the following disclosure which embodies several examples illustrative of our improved composition.

We have found that if there is incorporated in a substantially neutral aqueous stannous salt solutionor an aqueous solution of a mixture of stannous salts, or an aqueous solution of one or more stannous salts and a water-soluble sulfate-a relatively small amount of a water soluble aliphatic poly-hydroxy acid having at least one carboxyl group (COOH) and at least two hydroxy groups (OH), the resulting treating solution not only remains stable over long periods of time, but also that sludge formation is minimized and the treating solution lends itself both to automatic spraying procedures and immersion methods of treatment. Moreover, a concentrate consisting essentially of the stannous salt or mixture and the hydroxy acid, with or without a mineral acid or bulfer to insure the desired pH, may be bottled and stored indefinitely and need only be mixed with a prescribed amount of water to produce a satisfactory treating bath, thereby permitting an unskilled operator to make up the treating bath and practice the process.

In accordance with the present invention our improved treating composition consists essentially of an aqueous solution of a relatively pure substantially neutral stannous salt or mixture and from 0.1 to 50 parts or more, by weight, based on 100 parts of the stannous salt or mixture, of a water soluble aliphatic poly-hydroxy acid States Patent having at least one carboxyl group and at least two hydroxyl groups, such as tartaric, gluconic, glyceric, mucic, arabonic, galactonic, saccharic acids, mixtures of such acids, and their lactones, if existent. If desired, small amounts of mineral acids or buffers such as hydrochloric acid,-sulfuric acid, ammonium chloride, ammonium hydroxide, etc., may be added to produce a desired pH.

The optimum amount of hydroxy acid will vary for different formulations, and as the hydroxy acids have different degrees of effectiveness, more or less of one than of another may be required. For example, the effective range of tartaric acid when used with stannous chloride is from a minimum of approximately 0.1 part to a maximum which may exceed 20 parts by weight, based on the weight of parts of SnCl .2l-I O; whereas with gluconic acid the effective range may vary from 0.1 to 50 parts or more. As a general rule the effective range of the hydroxy acid will fall within that above specified, and in all cases there is an improvement in stability, corrosion resistance and density of color when the coating is subsequently dyed.

Although the various water soluble stannous salts may be used, as disclosed in Patent 2,478,954, practical considerations indicate the use of stannous chloride which may be prepared as a relatively pure substantially neutral concentrate as disclosed in the copending application of Walter A. Vittands, Serial No. 441,754 filed July 7, 1954. Such a concentrate contains 1 kilogram or more SHClz-ZHgO per liter of solution and the selected hydroxy acid or mixture of hydroxy acids or lactones may be added di-I rectly to the concentrate, along with a predetermined amount of buffering material when required by the contemplated use of the composition. The concentrate thus prepared may be bottled or put up in suitable containers until used, and in preparing a treating solution for general use the concentrate is mixed with water in an amount which may vary from 10 cc. to 1,000 cc. per liter of treating solution. The effectiveness of the treating solution may be increased by incorporating either in the concentrate or the treating solution prepared therefrom a compatible water-soluble sulfate salt, such as stannous sulfate, sodium sulfate, magnesium sulfate, or the like, in an amount which may vary from less than-20% up to 50% of the total salt content.

A specific example of a preferred procedure for preparing a stannous salt concentrate is as follows:

Example 1.A substantially neutral concentrate solution containing 1 kilogram of stannous chloride per liter is prepared either from a purified tin salt, or as set forth in the above-identified application of Walter A. Vittands, and to this concentrate is added 22 grams of tartaric acid per kilogram of SnCl .2H O in the form of a concentrated aqueous soluiton. The concentrate thus prepared may be bottled and stored indefinitely, and when used to provide a treating bath this concentrate is mixed with water in the proportion of 45 cc. of concentrate per liter of treating solution.

The bath thus prepared is ready for use as set forth in Example 1 of the aforementioned Patent 2,478,954. The resultant coating has improved corrosion resistance and an increased affinity for color when subsequently dyed. Moreover, the treating bath has 'a greater coverage, shows less sludge formation, and requires less supervision by the operator.

Example 2.-To one liter of an aqueous stannous chloride concentrate, prepared as set forth in Example 1, 44 grams of gluconic acid were added. The mixture was then diluted as in Example 1 to produce a treating bath whilrih gave a coating having the characteristics above set fort Example 3.. -The sameprocedure as set forth inExample 1 was followed, exceptthat 40 grams of delta-gluconolactone were used in place of the tartaric acid, and the same advantageous results were achieved.

Example '4.-The same procedure as set forth inExample 1 was followed, using 11 grams-of mucicacid in place of tartaricacid, and again the same advantageous results were achieved.

Example 5.'The same procedure as set forth in Example l was followed, using 28 grams .of glycericacid in place of the tartaric acid, and the same advantageous results were noted.

Example 6.--A treating bath containing 40 grams of stannous sulfaterand 3 grams of tartaric acid per liter was prepared and phosphated ferrous metal pieces were treated as in Example. 1 of Patent12,478,954. The resultant coating compared favorably with those of the preceding examples.

Example 7 An aqueous solution containing 106 grams of'stannousfluoborate (47% and lgram of tartaric acid, per liter, was prepared and used without dilution for treating phosp'hatedterrousarticles, as set forth in Example 1 of Patent 2,478,954. The solution showed a better stability on boiling and the pieces treated in it showed.

a better rust resistance than similar pieces treated in a bath without the tartaric .acid.

Examplel8.A solution as set forth in Example 1 was prepared by dissolving lOOOgrams of.SnCl .2H O crystals and 11 grams mucic .acid in water to 1 liter. A treating bath made of this concentrate in the usual way gives to the treated parts improved corrosion resistance and a better affinity for color when subsequently dyed than a bath without additional agent.

Example 9.To 1 liter of an aqueous solution containing 500 grams of SnCl .2H O and 480 grams of 'SnSO were added 11 grams of mucic acid. 45 ml. of this concentrate were diluted with water to 1 liter to provide a treating bath which is more effective than that of EX- ample 1.

Example 10. To 1 liter of an aqueous solution containing 750 grams SnCl .2H O and 240 grams of SnSO were added 22 grams of tartaric acid. This concentrate may be used in the same manner as that of Example 1 and is likewise more effective.

Concentrates or treating solutions may be prepared as set forthin Examples 9 and 10, substituting in whole or input other compatible water soluble sulfate salts or mixtures for the stannous sulfate component without materially lowering the effectiveness of the solution.

We claim:

1. The process of treating a metal article having an insoluble metal phosphate coating thereon produced by chemical reaction of the phosphate radical with the metal surface, which comprises subjecting said phosphate coating to theaction of an aqueous solution of a stannous salt and from 0.1 to 50 parts by weight, based on the weight of 100 parts of the stannous salt, of a water soluble aliphatic poly-hydroxy acid having at least one carboxyl group and at least two hydroxyl groups.

2. The process of treating a metal article having an insoluble metal phosphate coating thereon produced by chemical reaction of the phosphate radical with the metal surface, which comprises subjecting said phosphate coatingto the. action of an aqueous solution of a stannous chloride and from 0.1 to 50 parts by weight based on the weight of 100 parts of the stannous chloride of a water soluble hydroxy acid having at least one carboxyl group and at least two' hydroxyl groups. I i

3. The process of treating a metal article-having an in soluble metal phosphate coating thereon produced by chemical reaction of the phosphate radical withthe metal surface, which comprises subjecting said phosphate coating to the action of an aqueous solution of a stannous salt and from 0.1 to parts by weight, based on the weight of 100 parts of the stannous salt, of tartaric acid.

4. Theprocessfoftreating .a.metal .article having an insoluble metal phosphate coating thereon produced by chemical reaction of the phosphate radical with the metal surface, which comprises subjecting said phosphate coating to the action of an aqueous solution of stannous chloride and from 0.1 to 20 parts by weight, based on the weight of parts of the stannous chloride, of tartaric acid.

5. The process of treating a metal article having an insoluble metal phosphate coating thereon produced by chemical reaction of-the phosphate radical with the metal surface, which comprises subjecting said phosphate coating to the action of an aqueous solution of a stannous salt and from 0.1 to 50 parts by weight, based on the weight of 100 parts of the stannous salt, of gluconic acid.

6. The process of treating a metal article having an insoluble metal phosphate coating thereon produced by chemical reaction of the phosphate radical with the metal surface, whichcomprises subjecting said phosphate coating to the action of 'anaque'ous solution of a stannous'salt and from,0.1 to 50 parts by'weight, based on the weight of' 100 parts of the stannous salt, of mucic acid.

7. The process of treating a metal article having an insoluble metal phosphate coating thereon produced by chemical reaction ofthe'phosphate radical with the metal surface, which comprises subjecting said phosphate coating .to the action of an aqueous solution of a stannous salt and from 0.1 to 50 parts by weight, based'on the'weight of 100 parts of the stannous salt, of glyceric "acid.

8. The process of treating a metal article having an insoluble metal phosphate coating thereon produced by chemical reaction of'the phosphate radical with the metal surface, which comprises subjecting said phosphate coatingto'the action of anaqueous solution of a mixture of a stannous salt, a water-soluble sulfate salt in an amount less than the stannous salt and from 0.1 to 50 parts by weight, based on the weight of 100 parts of the stannous salt, of a water-soluble aliphatic poly-hydroxy acid having at least one carboxyl group and at least two hydroxyl groups.

9. The process of treating a-metal article having an insoluble metal phosphate coating-thereon produced by chemical reaction of the phosphate radical with the metal surface, which comprises subjecting said phosphate coating to the action of an aqueous solution of a mixture of a stannous salt and a water-soluble sulfate salt and from 0.1 to 50 parts by weight, based on the Weight of 100 parts of the stannous salt, of a water-soluble aliphatic polyhydroxy acid having at least one carboxyl group and at least two hydroxyl groups.

10. A composition for use in treating articles having a phosphate coating, consistingessentially of a water soluble stannous salt and from 0.1 to 50 parts by weight, based on the weight of 100 parts of the stannous salt, of a water soluble aliphatic poly-hydroxy acid having at least one carboxyl and at least two hydroxyl groups.

11. A composition for use in treating articles having a phosphate coating, consisting essentially of stannous chloride and from 0.1 to 50 parts by weight, based on the weight of 100 parts of the stannous chloride, of a water soluble aliphatic poly-hydroxy acid having at least one carboxyl and at least two hydroxyl groups.

12. A composition for use in treating articles having a phosphate coating, consisting essentially of a watersoluble stannous salt and from 0.1 to 20 parts by weight, based on the weight of 100 parts of the stannous salt, of tartaric acid.

13. A composition for use in treating articles having a phosphate coating, consisting essentially of stannous chloride and from 0.1 to 20 parts by weight, based on the weight of 100 partsof the stannous chloride, of tartaric acid.

14. A composition for use in treating articles having: phosphate coating, consisting essentially of a water soluble stannous salt and from 0.1to 50 parts by weight, based 5 on the weight of 100 parts of the stannous salt, of gluconic acid.

15. A composition for use in treating articles having a phosphate coating, consisting essentially of a water soluble stannous salt and from 0.1 to 50 parts by Weight, based on the weight of 100 parts of the stannous salt, of mucic acid.

16. A composition for use in treating articles having a phosphate coating, consisting essentially of a water soluble stannous salt and from 0.1 to 50 parts by weight, based on the Weight of 100 parts of the stannous salt, of glyceric acid.

17. A composition for use in treating articles having a phosphate coating, consisting essentially of a mixture of a water-soluble stannous salt, a water-soluble sulfate salt in an amount less than the stannous salt and from 0.1 to 50 parts by weight, based on the Weight of 100 parts of the stannous salt, of a water-soluble aliphatic poly-hydroxy acid having at least one carboxyl group and at least two hydroxyl groups.

18. A composition for use in treating articles having a phosphate coating, consisting essentially of a mixture of a References Cited in the file of this patent UNITED STATES PATENTS 2,343,569 Neeley et a1 Mar. 7, 1944 2,465,987 Gorman Apr. 5, 1949 2,478,954 Tuttle et a1. Aug. 16, 1949 2,516,139 Mazia July 25, 1950 FOREIGN PATENTS 615,911 Germany July 15, 1935 676,029 Germany May 24, 1939 

10. A COMPOSITION FOR USE IN TREATING ARTICLES HAVING A PHOSPHATE COATING, CONSISTING ESSENTIALLY OF A WATER SOLUBLE STANNOUS SALT AND FROM 0.1 TO 50 PARTS BY WEIGHT, BASED ON THE WEIGHT OF 100 PARTS OF THE STANNOUS SALT, OF A WATER SOLUBLE ALIPHATIC POLY-HYDROXY ACID HAVING AT LEAST ONE CARBOXYL AND AT LEAST TWO HYDROXYL GROUPS. 